Research On Compliant Control Strategy For Pneumatically Assisted Exoskeleton

In recent years,pneumatic artificial muscle(PAM)is becoming more and more popular.Due to its excellent characteristic,such as high force-to-mass ratio,small size,and simple arrangement,PAM has been widely applied in the exoskeleton area.In addition,PAM has many outstanding advantages,like being clean and environmentally friendly,lightweight,cheap and so on.Of course,PAM is also similar to human muscle as well as flexible.However,there is an obvious interactive force between human and exoskeleton during the movement.Furthermore,PAM has very strong nonlinearity.In order to achieve ideal human-exoskeleton collaboration and minimize the interactive force between human and exoskeleton,two key issues must be solved: 1.How to accurately predict the wearer's movement intention and obtain the wearer's movement trajectory;2.How to achieve a high-precision position control strategy for PAM with complex nonlinear characteristics,so that the exoskeleton can accurately and rapidly follow the movement of wearer,reducing the incoordination between human and exoskeleton.In this paper,the research object is the upper limb exoskeleton driven by PAM,s EMG is used to predict the human's movement intention.then the research on the human-exoskeleton compliance control strategy is carried out.The main work includes the following aspects:First of all,research focuses on designing the upper limb exoskeleton,including the arrangement of PAM,the installation of important sensors,selecting hardware for the control system,and designing the hardware architecture for the control system.Based on this platform,the system model is established,contributing to further study.Secondly,light is shed on the position control for PAM.The model of PAM has improved a lot by studying its hysteresis characteristic,lifting the performance of the control algorithm.In the beginning,the work concentrates on the related relationship between the pressure in PAM and PAM's position is studied.At this point,the proportional pressure valve is used as the driving valve and A model-free sliding mode control with compensation is proposed.Then,in order to achieve fast response and movement,the valve is replaced by the fast switching valve.Based on the study on the position-to-pressure relationship,the internal pressure loop is introduced,proposing a double closed-loop control strategy with compensation.At last,research makes a contribution to the human-exoskeleton compliance control strategy.The purpose of this strategy is to reduce the interactive force from the uncoordinated between the human and exoskeleton during movement.In this paper,s EMG is utilized to estimate the wearer's movement intention and predict the wearer's movement trajectory.Airbags are placed between the human and the exoskeleton,in which pressure reflects the interactive force between the human and exoskeleton.Furthermore,the change of pressure in the airbag is introduced to modify the predicted trajectory.Finally,through the posture control strategy,the exoskeleton can accurately and quickly follow the wearer's movement and achieve humanexoskeleton collaboration.The validity of the arithmetic is verified by related experiments.